This hint is for people trying to optimise their wireless signal reception in strange places. I recently had to get a wireless network operating over 100 meters away from the base station, and in a metal shed -- not the best environment for microwave communication!

This hint basically does the same job as AP Grapher, but can be run from the command line or over SSH -- so I was able to have someone else carry my MacBook Pro around the shed while I stayed near the wireless router and fiddled with its antennas.

I ssh'd into my MacBook Pro from a computer at the router, and ran the following command in Terminal:

This periodically displays the received signal strength indicator (RSSI), basically the power of the microwave radio signal from your router.

The value is in dBm, which is a logarithmic scale so that an increase of 10 units means a factor of 10 increase in power; an increase of 20 means a factor of 100 increase in power; etc. Watching this reading, I was able to position the router and antenna for maximum signal strength at various places in the shed.
The airport -I command alone displays other useful information about your airport connection, like the network name, channel, authorization mode, and the noise on the microwave signal.

Use a laptop as a mobile wireless power meter
Authored by: ALT147 on Apr 08, '10 05:56:31PM

Actually, they are microwaves, and, interestingly, they are at almost the same frequency (2.45 GHz) as those in your microwave oven. I'm not sure why that band was chosen.

But, in any case, the power present in your oven is in the hundreds of watts to kilowatts, whereas the power level sitting a metre away from a strong wireless router is less than -20 dBm, which is 0.00001 W. The power from the router I'm connected to now is -84 dBm, which is less than 0.00000000001 W. So we're probably OK.

Use a laptop as a mobile wireless power meter
Authored by: barko192 on Apr 08, '10 07:43:30PM

Just because EMR is in the microwave band, doesn't mean it will warm food. The 2.4 GHz and 5 GHz frequencies that wireless routers operate on are actually in the microwave band of 300 MHz to 300 GHz, the microwave band is a subset of the radio band of 3 kHz to 300 GHz.

Only microwaves of a specific frequency warm food, because the energy per microwave photon corresponds to a ro-vibronic energy transition in the water molecule.

Use a laptop as a mobile wireless power meter
Authored by: ALT147 on Apr 11, '10 03:51:26PM

Only microwaves of a specific frequency warm food, because the energy per microwave photon corresponds to a ro-vibronic energy transition in the water molecule.

In fact, microwaves of anywhere from 1 GHz to a few hundred GHz will warm food. See this page for far too much detail. I just thought it odd that the frequency of a microwave oven coincided with channels 7, 8 and 9 of the 802.11 standard. Even though the power levels may be way too low to heat anything (or anyone), surely you'd choose a band far away from any commonplace, powerful source like a microwave oven for the sake of interference?

Use a laptop as a mobile wireless power meter
Authored by: ALT147 on Apr 11, '10 04:04:51PM

I was using a Belkin F5D8236-4 N wireless router, but not by choice, and I wouldn't recommend it. You can't even set an administrator password on it.

The question of signal strength is interesting. I'd advise you to check it out for yourself using the airport -I command in various places (note that the reported RSSI doesn't respond instantly to a change in signal strength, and the airport signal icon in the menubar is even more delayed). The signal I got at the other end of the shed was about -60 to -70 dBm, which is a signal-to-noise ratio of 20-30 dB, or 100 to 1000.

The signal on the network I'm using right now is at -83 dBm, a signal-to-noise ratio of only 5 dB = 3 (there's about -88 dBm of noise), but I still have full reception according to the airport icon in the menubar. If I go further away from the router, the SNR drops to 0 dB (as much signal as noise), but the airport icon still reports 2 bars.